Emulated storage system

ABSTRACT

A method for removing redundant data from a backup storage system is presented. In one example, the method may include identifying a first back-up data object, identifying a second back-up data object, detecting a first portion of the first back-up data object that is a copy of a second portion of the second back-up data object, and replacing the second portion with a pointer to the first portion.

RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority under35 U.S.C. §120 to, pending U.S. patent application Ser. No. 11/593,266filed Nov. 6, 2006, entitled “Emulated Storage System,” which is acontinuation of, and claims priority under 35 U.S.C. §120 to, U.S.patent application Ser. No. 10/911,987, filed Aug. 5, 2004, entitled“Emulated Storage System” and now U.S. Pat. No. 7,146,476, which claimsthe benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No.60/492,576, entitled “Synthetic Full Back-up Method,” filed on Aug. 5,2003 and U.S. Provisional Application No. 60/492,827, entitled “End-UserFile Restore Method,” filed on Aug. 6, 2003, each of which is herebyincorporated by reference in its entirety.

BACKGROUND

1. Field of Invention

Aspects of the present invention relate to data storage, and moreparticularly to apparatus and methods for emulating a tape storagesystem which can provide the equivalent of full data back-ups using anexisting full back-up and subsequent incremental back-ups and enablingend-users to restore data from such back-ups.

2. Discussion of Related Art

Many computer systems include one or more host computers and one or moredata storage systems that store data used by the host computers. Thesehost computers and storage systems are typically networked togetherusing a network such as a Fibre Channel network, an Ethernet network, oranother type of communication network. Fibre Channel is a standard thatcombines the speed of channel-based transmission schemes and theflexibility of network-based transmission schemes and allows multipleinitiators to communicate with multiple targets over a network, wherethe initiator and the target may be any device coupled to the network.Fibre Channel is typically implemented using a fast transmission mediasuch as optical fiber cables, and is thus a popular choice for storagesystem networks where large amounts of data are transferred.

An example of a typical networked computing environment includingseveral host computers and back-up storage systems is shown in FIG. 1.One or more application servers 102 are coupled via a local area network(LAN) 103 to a plurality of user computers 104. Both the applicationservers 102 and the user computers 104 may be considered “hostcomputers.” The application servers 102 are coupled to one or moreprimary storage devices 106 via a storage area network (SAN) 108. Theprimary storage devices 106 may be, for example, disk arrays such as areavailable from companies like EMC Corporation, IBM Corporation andothers. Alternatively, a bus (not shown) or other network link mayprovide an interconnect between the application servers and the primarystorage system 106. The bus and/or Fibre Channel network connection mayoperate using a protocol, such as the Small Component SystemInterconnect (SCSI) protocol, which dictates a format of packetstransferred between the host computers (e.g., the application servers102) and the storage system(s) 106.

It is to be appreciated that the networked computing environmentillustrated in FIG. 1 is typical of a large system as may be used by,for example, a large financial institution or large corporation. It isto be understood that many networked computing environments need notinclude all the elements illustrated in FIG. 1. For example, a smallernetworked computing environment may simply include host computersconnected directly, or via a LAN, to a storage system. In addition,although FIG. 1 illustrates separate user computers 104, applicationservers 102 and media servers 114, these functions may be combined intoone or more computers.

In addition to primary storage devices 106, many networked computerenvironments include at least one secondary or back-up storage system110. The back-up storage system 110 may typically be a tape library,although other large capacity, reliable secondary storage systems may beused. Typically, these secondary storage systems are slower than theprimary storage devices, but include some type of removable media (e.g.,tapes, magnetic or optical disks) that may be removed and storedoff-site.

In the illustrated example, the application servers 102 may be able tocommunicate directly with the back-up storage system 110 via, forexample, an Ethernet or other communication link 112. However, such aconnection may be relatively slow and may also use up resources, such asprocessor time or network bandwidth. Therefore, a system such asillustrated may include one or more media servers 114 that may provide acommunication link 115, using for example, Fibre Channel, between theSAN 108 and the back-up storage system 110.

The media servers 114 may run software that includes a back-up/restoreapplication that controls the transfer of data between host computers(such as user computers 104, the media servers 114, and/or theapplication servers 102), the primary storage devices 106 and theback-up storage system 110. Examples of back-up/restore applications areavailable from companies like Veritas, Legato and others. For dataprotection, data from the various host computers and/or the primarystorage devices in a networked computing environment may be periodicallybacked-up onto the back-up storage system 110 using a back-up/restoreapplication, as is known in the art.

Of course, it is to be appreciated that, as discussed above, manynetworked computer environments may be smaller and may include fewercomponents than does the exemplary networked computer environmentillustrated in FIG. 1. Therefore, it is also to be appreciated that themedia servers 114 may in fact be combined with the application servers102 in a single host computer, and that the back-up/restore applicationmay be executed on any host computer that is coupled (either directly orindirectly, such as through a network) to the back-up storage system110.

One example of a typical back-up storage system is a tape library thatincludes a number of tape cartridges and at least one tape drive, and arobotic mechanism that controls loading and unloading of the cartridgesinto the tape drives. The back-up/restore application providesinstructions to the robotic mechanism to locate a particular tapecartridge, e.g., tape number 0001, and load the tape cartridge into thetape drive so that data may be written onto the tape. Theback-up/restore application also controls the format in which data iswritten onto the tapes. Typically, the back-up/restore application mayuse SCSI commands, or other standardized commands, to instruct therobotic mechanism and to control the tape drive(s) to write data ontothe tapes and to recover previously written data from the tapes.

Conventional tape library back-up systems suffer from a number ofproblems including speed, reliability and fixed capacity. Many largecompanies need to back-up Terabytes of data each week. However, evenexpensive, high-end tapes can usually only read/write data at speeds of30-40 Megabytes per second (MB/s), which translates to about 50 Gigabyteper hour (GB/hr). Thus, to back-up one or two Terabytes of data to atape back-up system may take at least 10 to 20 hours of continuous datatransfer time.

In addition, most tape manufacturers will not guarantee that it will bepossible to store (or restore) data to/from a tape if the tape isdropped (as may happen relatively frequently in a typical tape librarybecause either a human operator or the robotic mechanism may drop a tapeduring a move or load operation) or if the tape is exposed to non-idealenvironmental conditions, such as extremes in temperature or moisture.Therefore, a great deal of care needs to be taken to store tapes in acontrolled environment. Furthermore, the complex machinery of a tapelibrary (including the robotic mechanism) is expensive to maintain andindividual tape cartridges are relatively expensive and have limitedlifespans.

SUMMARY OF INVENTION

Embodiments of the present invention provide a back-up storage systemthat overcomes or alleviates some or all of the problems of conventionaltape library systems and that may provide greater flexibility than doconventional tape library systems.

In broad overview, aspects and embodiments of the present inventionprovide a random-access based storage system that emulates aconventional tape back-up storage system such that a back-up/restoreapplication sees the same view of devices and media as with a physicaltape library. The storage system of the invention uses software andhardware to emulate physical tape media and replace them with one ormore random-access disk arrays, translating tape format, linear,sequential data to data that is suitable for storage on disk.

According to some aspects and embodiments of the present invention,there is provided a mechanism for decoding existing back-up data setsand storing the metadata (i.e., data that represents information aboutuser data) in a searchable metadata cache, a mechanism to allowsearching and/or viewing of the metadata cache for files or objects, anda mechanism for downloading these files or objects via a web connectionfrom data stored through existing back-up policies and practices oftypical back-up software. Also included may be a mechanism forauthenticating a user through existing authentication mechanisms, andfor limiting the view of the metadata cache based on a current user'scredentials.

Aspects and embodiments of the present invention also provide forremoval of redundant data from back-up data objects. This removalprocess, which may be termed “de-duplication,” decreases the storagecapacity required to maintain copies of back-up data and thus decreasesthe amount of electronic media required to store back-up data.Embodiments of the de-duplication process in accordance with at leastsome aspects of the present invention make efficient use of computingresources by using metadata to optimize de-duplication processing, asdiscussed further below.

According to other aspects and embodiments of the invention, there isprovided a mechanism for performing a logical merge of multiplecartridge representations in a metadata cache, and a mechanism forappropriately labeling and barcoding a newly synthesized cartridge suchthat it is accepted by back-up/restore software as a valid data set.Also, according to further aspects and embodiments of the invention,there is provided a mechanism for either storing multiple copies of dataelements that represent a synthetic cartridge, or for storing onlypointers to existing data represented in the metadata cache.

One aspect of the invention is directed toward a method for removingredundant data from a backup storage system that includes identifying afirst back-up data object, identifying a second back-up data object,detecting a first portion of the first back-up data object that is acopy of a second portion of the second back-up data object and replacingthe second portion with a pointer to the first portion.

In the method, replacing the second portion with the pointer to thefirst portion may include creating a copy of the second back-up dataobject excluding the second portion, including a pointer to the firstportion and deleting the second back-up data object.

The method may also include validating that the copy of the secondback-up data object represents the same data as the second back-up dataobject. In the method, identifying the second back-up data object mayinclude identifying a second back-up data object that was backed-up lessrecently than the first back-up data object. In the method, identifyingthe second back-up data object may include identifying a second back-updata object that was backed-up more recently than the first back-up dataobject.

The method may also include identifying at least one characteristic ofdata object metadata. In the method, identifying the first back-up dataobject may include identifying a first back-up data object associatedwith data object metadata having the at least one characteristic. Alsoin the method, identifying the second back-up data object may includeidentifying a second back-up data object associated with data objectmetadata having the at least one characteristic.

In the method, identifying at least one characteristic of data objectmetadata may include identifying a location in primary storageassociated with the first back-up data object and identifying a locationin primary storage associated with the second back-up data object. Inthe method, identifying at least one characteristic of data objectmetadata may include identifying a software application associated withthe first back-up data object and identifying a software applicationassociated with the second back-up data object. In the method,identifying at least one characteristic of data object metadata mayinclude identifying a back-up policy associated with the first back-updata object and identifying a back-up policy associated with the secondback-up data object.

In the method, identifying at least one characteristic of data objectmetadata may include identifying at least one characteristic of dataobject metadata that was stored while the first back-up data object wasbeing backed-up and identifying at least one characteristic of dataobject metadata that was stored while the second back-up data object wasbeing backed-up. In the method, detecting the first portion of the firstback-up data object may include detecting the first portion of the firstback-up data object using metadata associated with the first back-updata object and metadata associated with the second back-up data object.In the method detecting the first portion of the first back-up dataobject using metadata may include detecting the first portion of thefirst back-up data object using metadata stored in a relationaldatabase. In the method, identifying the first back-up data object mayinclude identifying a first data file and identifying the second back-updata object may include identifying a second data file. The method maybe executed in a grid computing environment. The method may be executedon a back-up storage system while data is not being backed-up to theback-up storage system.

Another aspect of the invention is directed toward a computer-readablemedium having computer-readable signals stored thereon that defineinstructions that, as a result of being executed by a computer, instructthe computer to identify a first back-up data object, identify a secondback-up data object, detect a first portion of the first back-up dataobject that is a copy of a second portion of the second back-up dataobject and replace the second portion with a pointer to the firstportion.

Another aspect of the invention is directed toward a method thatincludes identifying a first data object associated with a softwareapplication, identifying a second data object associated with thesoftware application, detecting, using a pattern of data distributionassociated with the software application, redundant data in both thefirst data object and the second data object and replacing the redundantdata in the first data object with a pointer to the redundant datadisposed in the second data object.

Another aspect of the invention is directed toward a computer-readablemedium having computer-readable signals stored thereon that defineinstructions that, as a result of being executed by a computer, instructthe computer to identify a first data object associated with a softwareapplication, identify a second data object associated with the softwareapplication, detect, using a pattern of data distribution associatedwith the software application, redundant data in both the first dataobject and the second data object and replace the redundant data in thefirst data object with a pointer to the redundant data disposed in thesecond data object.

Another aspect of the invention is directed toward a system thatincludes back-up storage media storing a plurality of back-up dataobjects including a first back-up data object including first data and asecond back-up data object including second data and a controllerconfigured to identify any portion of the second data that is the sameas any portion of the first data, and to replace an identified portionof the second data with a pointer to a corresponding portion of thefirst data.

In the system, the controller may be further configured to replace anidentified portion of the second data object by creating a copy of thesecond data object excluding the identified portion and including apointer to the corresponding portion of the first data.

Another aspect of the invention is directed toward a method thatincludes identifying at least one characteristic of data objectmetadata, identifying a first back-up data object associated with dataobject metadata having the at least one characteristic, identifying asecond back-up data object associated with data object metadata havingthe at least one characteristic, detecting redundant data in both thefirst back-up data object and the second back-up data object, creating acopy of the second back-up data object excluding at least one instanceof the redundant data wherein the copy includes a pointer to theredundant data instead of the excluded as least one instance of theredundant data and deleting the second back-up data object.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments, and are intended to provide an overview or frameworkfor understanding the nature and character of the claimed aspects andembodiments. The accompanying drawings are included to provideillustration and a further understanding of the various aspects andembodiments, and are incorporated in and constitute a part of thisspecification. The drawings, together with the remainder of thespecification, serve to explain principles and operations of thedescribed and claimed aspects and embodiments.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures. In the figures, which are notintended to be drawn to scale, each identical or nearly identicalcomponent that is illustrated in various figures is represented by alike numeral. For purposes of clarity, not every component may belabeled in every drawing. The figures are provided for the purposes ofillustration and explanation and are not intended as a definition of thelimits of the invention. In the figures:

FIG. 1 is a block diagram of one example of a large-scale networkedcomputing environment that includes a back-up storage system;

FIG. 2 is a block diagram of one embodiment of a networked computingenvironment including a storage system according to aspects of theinvention;

FIG. 3 is a block diagram of one embodiment of a storage systemaccording to aspects of the invention;

FIG. 4 is a block diagram illustrating a virtual layout of oneembodiment of a storage system according to aspects of the invention;

FIG. 5 is a schematic layout of one example of a system file accordingto aspects of the invention;

FIG. 6 is one example of a tape directory structure according to aspectsof the invention;

FIG. 7 is a diagram depicting one example of a method of creating asynthetic full back-up according to aspects of the invention;

FIG. 8 is a schematic diagram of one example, of a series of back-updata sets including a synthetic full back-up according to aspects of theinvention;

FIG. 9 is a diagram of one example, of a metadata cache structure;

FIG. 10 is a diagram of one example of a virtual cartridge storing asynthetic full back-up data set;

FIG. 11 is a diagram of another examples of a virtual cartridge storinga synthetic full back-up data set;

FIG. 12 is a flow diagram of a method of de-duplicating data objects inaccordance with the present invention;

FIG. 13A is a diagram of two back-up data objects;

FIG. 13B is a diagram of de-duplicated copies of the back-up dataobjects depicted in FIG. 13A; and

FIG. 13C is another diagram of de-duplicated copies of the back-up dataobjects depicted in FIG. 13A.

DETAILED DESCRIPTION

Various embodiments and aspects thereof will now be described in moredetail with reference to the accompanying figures. It is to beappreciated that this invention is not limited in its application to thedetails of construction and the arrangement of components set forth inthe following description or illustrated in the drawings. The inventionis capable of other embodiments and of being practiced or of beingcarried out in various ways. Examples of specific implementations areprovided herein for illustrative purposes only and are not intended tobe limiting. In particular, acts, elements and features discussed inconnection with any one or more embodiments are not intended to beexcluded from a similar role in any other embodiments. Also, thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

As used herein, the term “host computer” refers to any computer that hasat least one processor, such as a personal computer, a workstation, amainframe, a networked client, a server, etc. that is capable ofcommunication with other devices, such as a storage system or other hostcomputers. Host computers may include media servers and applicationservers (as described previously with reference to FIG. 1) as well asuser computers (which may be user workstations, PCs, mainframes, etc.).In addition, within this disclosure, the term “networked computerenvironment” includes any computing environment in which a plurality ofhost computers are connected to one or more shared storage systems insuch a manner that the storage system(s) can communicate with each ofthe host computers. Fibre Channel is one example of a communicationnetwork that may be used with embodiments of the present invention.However, it is to be appreciated that the networks described herein arenot limited to Fibre Channel, and that the various network componentsmay communicate with each other over any network connection, such asToken Ring or Ethernet instead of, or in addition to Fibre Channel, orover combinations of different network connections. Moreover, aspects ofthe present invention may also be used in bus topologies, such as SCSIor parallel SCSI.

According to various embodiments and aspects of the present invention,there is provided a virtual removable media library back-up storagesystem that may use one or more disk arrays to emulate a removable mediabased storage system. Using embodiments of the invention, data may bebacked-up onto the disk array(s) using the same back-up/restoreapplication as would have been used to back-up the data onto removablemedia (such as tapes, magnetic disks, optical disks, etc.), without auser having to make any modifications or adjustments to the existingback-up procedures or having to purchase a new back-up/restoreapplication. In one embodiment, described in detail herein, theremovable media that are emulated are tapes, and the back-up storagesystem of the invention emulates a tape library system including tapesand the robotic mechanism used to handle tapes in a conventional tapelibrary system.

The data that may be backed-up and restored using embodiments of theinvention may be organized into various data objects. These data objectsmay include any structure into which data may be stored. A non-limitinglist of exemplary data objects includes bits, bytes, data files, datablocks, data directories, back-up data sets and virtual cartridges,which are discussed further below. Although the bulk of this disclosurerefers to back-up and restore of data files, embodiments of theinvention may manipulate any data object and it is to be appreciatedthat the term “data file” is interchangeable with “data object.”

A storage system according to aspects of the invention includes hardwareand software that together interface with a host computer (running theback-up/restore application) and a back-up storage media. The storagesystem may be designed to emulate tapes, or other types of removablestorage media, such that the back-up/restore application sees the sameview of devices and media as with a physical tape library, and totranslate linear, sequential, tape format data into data that issuitable for storage on random-access disks. In this manner, the storagesystem of the invention may provide enhanced functionality (such as,allowing users to search for individual back-up user files, as discussedbelow) without requiring new back-up/restore application software orpolicies.

Referring to FIG. 2, there is illustrated in block diagram form, oneembodiment of a networked computing environment including a back-upstorage system 170 according to aspects of the invention. Asillustrated, a host computer 120 is coupled to the storage system 170via a network connection 121. This network connection 121 may be, forexample a Fibre Channel connection to allow high-speed transfer of databetween the host computer 120 and the storage system 170. It is to beappreciated that the host computer 120 may be, or may include, one ormore application servers 102 (see FIG. 1) and/or media servers 114 (seeFIG. 1) and may enable back-up of data from either any of the computerspresent in the networked computing environment or from a primary storagedevice 106 (see FIG. 1). In addition, one or more user computers 136 mayalso be coupled to the storage system 170 via another network connection138, such as an Ethernet connection. As discussed in detail below, thestorage system may enable users of the user computer 136 to view andoptionally restore back-up user files from the storage system.

The storage system includes back-up storage media 126 that may be, forexample, one or more disk arrays, as discussed in more detail below. Theback-up storage media 126 provide the actual storage space for back-updata from the host computer(s) 120. However, the storage system 170 mayalso include software and additional hardware that emulates a removablemedia storage system, such as a tape library, such that, to theback-up/restore application running on the host computer 120, it appearsas though data is being backed-up onto conventional removable storagemedia. Thus, as illustrated in FIG. 2, the storage system 170 mayinclude “emulated media” 134 which represent, for example, virtual oremulated removable storage media such as tapes. These “emulated media”134 are presented to the host computer by the storage system softwareand/or hardware and appear to the host computer 120 as physical storagemedia. Further interfacing between the emulated media 134 and the actualback-up storage media 126 may be a storage system controller (not shown)and a switching network 132 that accepts the data from the host computer120 and stores the data on the back-up storage media 126, as discussedmore fully in detail below. In this manner, the storage system“emulates” a conventional tape storage system to the host computer 120.

According to one embodiment, the storage system may include a “logicalmetadata cache” 242 that stores metadata relating to user data that isbacked-up from the host computer 120 onto the storage system 170. Asused herein, the term “metadata” refers to data that representsinformation about user data and describes attributes of actual userdata. A non-limiting exemplary list of metadata regarding data objectsmay include data object size, logical and/or physical location of thedata object in primary storage, the creation date of the data object,the date of the last modification of the data object, the back-up policyname under which the data objected was stored, an identifier, e.g. aname or watermark, of the data object and the data type of the dataobject, e.g. a software application associated with the data object. Thelogical metadata cache 242 represents a searchable collection of datathat enables users and/or software applications to randomly locateback-up user files, compare user files with one another, and otherwiseaccess and manipulate back-up user files. Two examples of softwareapplications that may use the data stored in the logical metadata cache242 include a synthetic full back-up application 240 and an end-userrestore application 300 that are discussed more fully below.

In brief overview, the synthetic full back-up application 240 is capableof creating a synthetic full back-up data set from one existing fullback-up data set and one or more incremental back-up data sets. Thesynthetic full backup may obviate the need to perform periodic (e.g.,weekly) full back-ups, thereby saving considerable time and networkresources. Details of the synthetic full back-up application 240 aredescribed further below. The end-user restore application 300, alsodescribed more fully in detail below, enables end-users (e.g., operatorsof the user computers 136) to browse, locate, view and/or restorepreviously backed-up user files from the storage system 170.

As discussed above, the storage system 170 includes hardware andsoftware that interface with the host computer 120 and the back-upstorage media 126. Together, the hardware and software of embodiments ofthe invention may emulate a conventional tape library back-up systemsuch that, from the point of view of the host computer 120, data appearsto be backed-up onto tape, but is in fact backed-up onto another storagemedium, such as, for example, a plurality of disk arrays.

Referring to FIG. 3, there is illustrated in block diagram form, oneembodiment of a storage system 170 according to aspects of theinvention. In one example, the hardware of the storage system 170includes a storage system controller 122 and a switching network 132that connects the storage system controller 122 to the back-up storagemedia 126. The storage system controller 122 includes a processor 127(which may be a single processor or multiple processors) and a memory129 (such as RAM, ROM, PROM, EEPROM, Flash memory, etc. or combinationsthereof) that may run all or some of the storage system software. Thememory 129 may also be used to store metadata relating to the datastored on the back-up storage media 126. Software, including programmingcode that implements embodiments of the present invention, is generallystored on a computer readable and/or writeable nonvolatile recordingmedium, such as RAM, ROM, optical or magnetic disk or tape, etc., andthen copied into memory 129 wherein it may then be executed by theprocessor 127. Such programming code may be written in any of aplurality of programming languages, for example, Java, Visual Basic, C,C#, or C++, Fortran, Pascal, Eiffel, Basic, COBAL, or combinationsthereof, as the present invention is not limited to a particularprogramming language. Typically, in operation, the processor 127 causesdata, such as code that implements embodiments of the present invention,to be read from a nonvolatile recording medium into another form ofmemory, such as RAM, that allows for faster access to the information bythe processor than does the nonvolatile recording medium.

As shown in FIG. 3, the controller 122 also includes a number of portadapters that connect the controller 122 to the host computer 120 and tothe switching network 132. As illustrated, the host computer 120 iscoupled to the storage system via a port adapter 124 a, which may be,for example, a Fibre Channel port adapter. Via a storage systemcontroller 122, the host computer 120 backs up data onto the back-upstorage media 126 and can recover data from the back-up storage media126.

In the illustrated example, the switching network 132 may include one ormore Fibre Channel switches 128 a, 128 b. The storage system controller122 includes a plurality of Fibre Channel port adapters 124 b and 124 cto couple the storage system controller to the Fibre Channel switches128 a, 128 b. Via the Fibre Channel switches 128 a, 128 b, the storagesystem controller 122 allows data to be backed-up onto the back-upstorage media 126. As illustrated in FIG. 3, the switching network 132may further include one or more Ethernet switches 130 a, 130 b that arecoupled to the storage system controller 122 via Ethernet port adapters125 a, 125 b. In one example, the storage system controller 122 furtherincludes another Ethernet port adapter 125 c that may be coupled to, forexample, a LAN 103 to enable the storage system 170 to communicate withhost computes (e.g., user computers), as discussed below.

In the example illustrated in FIG. 3, the storage system controller 122is coupled to the back-up storage media 126 via a switching network thatincludes two Fibre Channel switches and two Ethernet switches. Provisionof at least two of each type of switch within the storage system 170eliminates any single points of failure in the system. In other words,even if one switch (for example, Fibre Channel switch 128 a) were tofail, the storage system controller 122 would still be able tocommunicate with the back-up storage media 126 via another switch. Suchan arrangement may be advantageous in terms of reliability and speed.For example, as discussed above, reliability is improved throughprovision of redundant components and elimination of single points offailure. In addition, in some embodiments, the storage system controlleris able to back-up data onto the back-up storage media 126 using some orall of the Fibre Channel switches in parallel, thereby increasing theoverall back-up speed. However, it is to be appreciated that there is norequirement that the system comprise two or more of each type of switch,nor that the switching network comprise both Fibre Channel and Ethernetswitches. Furthermore, in examples wherein the back-up storage media 126comprises a single disk array, no switches at all may be necessary.

As discussed above, in one embodiment, the back-up storage media 126 mayinclude one or more disk arrays. In one preferred embodiment, theback-up storage media 126 include a plurality of ATA or SATA disks. Suchdisks are “off the shelf” products and may be relatively inexpensivecompared to conventional storage array products from manufacturers suchas EMC, IBM, etc. Moreover, when one factors in the cost of removablemedia (e.g., tapes) and the fact that such media have a limitedlifetime, such disks are comparable in cost to conventional tape-basedback-up storage systems. In addition, such disks can read/write datasubstantially faster than can tapes. For example, over a single FibreChannel connection, data can be backed-up onto a disk at a speed of atleast about 150 MB/s, which translates to about 540 GB/hr, significantlyfaster (e.g., by an order of magnitude) than tape back-up speeds. Inaddition, several Fibre Channel connections may be implemented inparallel, thereby increasing the speed even further. In accordance withan embodiment of the present invention, back-up storage media may beorganized to implement any one of a number of RAID (Redundant Array ofIndependent Disks) schemes. For example, in one embodiment, the back-upstorage media may implement a RAID-5 implementation.

As discussed above, embodiments of the invention emulate a conventionaltape library back-up system using disk arrays to replace tape cartridgesas the physical back-up storage media, thereby providing a “virtual tapelibrary.” Physical tape cartridges that would be present in aconventional tape library are replaced by what is termed herein as“virtual cartridges.” It is to be appreciated that for the purposes ofthis disclosure, the term “virtual tape library” refers to an emulatedtape library which may be implemented in software and/or physicalhardware as, for example, one or more disk array(s). It is further to beappreciated that although this discussion refers primarily to emulatedtapes, the storage system may also emulate other storage media, forexample, a CD-ROM or DVD-ROM, and that the term “virtual cartridge”refers generally to emulated storage media, for example, an emulatedtape or emulated CD. In one embodiment, the virtual cartridge in factcorresponds to one or more hard disks.

Therefore, in one embodiment, a software interface is provided toemulate the tape library such that, to the back-up/restore application,it appears that the data is being backed-up onto tape. However, theactual tape library is replaced by one or more disk arrays such that thedata is in fact being backed-up onto these disk array(s). It is to beappreciated that other types of removable media storage systems may beemulated and the invention is not limited to the emulation of tapelibrary storage systems. The following discussion will now explainvarious aspects, features and operation of the software included in thestorage system 170.

It is to be appreciated that although the software may be described asbeing “included” in the storage system 170, and may be executed by theprocessor 127 of the storage system controller 122 (see FIG. 3), thereis no requirement that all the software be executed on the storagesystem controller 122. The software programs such as the synthetic fullback-up application and the end-user restore application may be executedon the host computers and/or user computers and portions thereof may bedistributed across all or some of the storage system controller, thehost computer(s), and the user computer(s). Thus, it is to beappreciated that there is no requirement that the storage systemcontroller be a contained physical entity such as a computer. Thestorage system 170 may communicate with software that is resident on ahost computer such as, for example, the media server(s) 114 orapplication servers 102. In addition, the storage system may containseveral software applications that may be run or resident on the same ordifferent host computers. Moreover, it is to be appreciated that thestorage system 170 is not limited to a discrete piece of equipment,although in some embodiments, the storage system 170 may be embodied asa discrete piece of equipment. In one example, the storage system 170may be provided as a self-contained unit that acts as a “plug and play”(i.e., no modification need be made to existing back-up procedures andpolicies) replacement for conventional tape library back-up systems.Such a storage system unit may also be used in a networked computingenvironment that includes a conventional back-up system to provideredundancy or additional storage capacity. In another embodiment, thestorage system 116 may be implemented in a distributed computingenvironment, such as a clustered or a grid environment.

As discussed above, according to one embodiment, the host computer 120(which may be, for example, an application server 102 or media server114, see FIG. 1) may back-up data onto the back-up storage media 126 viathe network link (e.g., a Fibre Channel link) 121 that couples the hostcomputer 120 to the storage system 170. It is to be appreciated thatalthough the following discussion will refer primarily to the back-up ofdata onto the emulated media, the principles apply also to restoringback-up data from the emulated media. The flow of data between the hostcomputer 120 and the emulated media 134 may be controlled by theback-up/restore application, as discussed above. From the view point ofthe back-up/restore application, it may appear that the data is actuallybeing backed-up onto a physical version of the emulated media.

Referring to FIG. 4, the storage system software 150 may include one ormore logical abstraction layer(s) that represent the emulated media andprovide an interface between a back-up/restore application 140 residenton the host computer 120 and the back-up storage media 126. The software150 accepts tape format data from the back-up/restore application 140and translates that data into data suitable for storage on random-accessdisks (e.g., hard disks, optical disks and the like). In one example,this software 150 is executed on the processor 127 of the storage systemcontroller 122 and may be stored in memory 129 (see FIG. 3).

According to one embodiment, the software 150 may include a layer,referred to herein as the virtual tape library (VTL) layer 142 that mayprovide a SCSI emulation of tapes, tape drives, and also the roboticmechanisms used to transfer tapes to and from the tape drives. Theback-up/restore application 140 may communicate (e.g., back-up or writedata to the emulated media) with the VTL 142 using, for example, SCSIcommands, represented by arrows 144. Thus, the VTL may form a softwareinterface between the other storage system software and hardware and theback-up/restore application, presenting the emulated storage media 134(FIG. 2) to a back-up/restore application and allowing the emulatedmedia to appear to the back-up/restore application as conventionalremovable back-up storage media.

A second software layer referred to herein as the file system layer 146may provide an interface between the emulated storage media (representedin the VTL) and the physical back-up storage media 126. In one example,the file system, 146 acts as a mini operating system to communicate withthe back-up storage media 126 using, for example, SCSI commands,represented by arrows 148, to read and write data to and from theback-up storage media 126.

In one embodiment, the VTL provides generic tape library support and maysupport any SCSI media changer. Emulated tape devices may include, butare not limited to, an IBM LTO-1 and LTO-2 tape device, a QUANTUMSuperDLT320 tape device, a QUANTUM P3000 tape library system, or aSTORAGETEK L180 tape library system. Within the VTL, each virtualcartridge is a file that may grow dynamically as data is stored. This isin contrast to conventional tape cartridges which have a fixed size. Oneor more virtual cartridges may be stored in a system file as describedfurther below with respect to FIG. 5.

FIG. 5 illustrates one example of a data structure within the filesystem software 146 that illustrates a system file 200 in accordancewith an embodiment of the present invention. In this embodiment, thesystem file 200 includes a header 202 and data 204. The header 202 mayinclude information that identifies each of the virtual cartridges thatare stored in that system file. The header may also contain informationsuch as, whether a virtual cartridge is write protected, the dates ofcreation/modification of the virtual cartridges, etc. In one example,the header 202 includes information uniquely identifying each virtualcartridge and distinguishing each virtual cartridge from other virtualcartridges stored in the storage system. For example, this informationmay include a name and an identifying number (corresponding to a barcodethat would typically be present on a physical tape so that the tapecould be identified by the robotic mechanism) of the virtual cartridge.The header 202 may also contain additional information such as acapacity of each of the virtual cartridges, a date of last modification,etc.

According to one embodiment of the present invention, the size of theheader 202 may be optimized to reflect the type of data being stored(e.g., virtual cartridges representing data back-up from one or morehost computer systems) and the number of distinct sets of such data(e.g., virtual cartridges) that the system can track. For example, datathat is typically backed-up to a tape storage system is typicallycharacterized by larger data sets representing numerous system and userfiles. Because the data sets are so large, the number of discrete datafiles to be tracked may be correspondingly small. Accordingly, in oneembodiment, the size of the header 202 may selected based on acompromise between storing too much data to efficiently keep track of(i.e., the header being too big) and not having space to store asufficient number of cartridge identifiers (i.e., header being toosmall). In one exemplary embodiment, the header 202 utilizes the first32 MB of the system file 200. However it is to be appreciated that theheader 202 may have a different size based on system needs andcharacteristics and that, depending on system needs and capacity, onemay select a different size for the header 202.

It is to be appreciated that, from the point of view of theback-up/restore application, the virtual cartridges appear as physicaltape cartridges with all the same attributes and features. That is, tothe back-up restore application, the virtual cartridges appear assequentially written tapes. However, in one preferred embodiment, thedata stored in the virtual cartridges is not stored in a sequentialformat on back-up storage media 126. Rather, the data that appears to bewritten to the virtual cartridges is in fact stored in the storagesystem's files as randomly accessible, disk-format data. Metadata isused to link the stored data to virtual cartridges so that theback-up/restore application can read and write data in cartridge format.

Thus, in broad overview of one preferred embodiment, user and/or systemdata (referred to herein as “file data”) is received by the storagesystem 170 from the host computer 120 and is stored on the disk array(s)making up the back-up storage media 126. The software 150 (see FIG. 4)and/or hardware of the storage system writes this file data to theback-up storage media 126 in the form of system files, as is describedin more detail below. Metadata is extracted as the data file is beingbacked-up by the storage system controller to keep track of attributesof the user and/or system files that are backed-up. For example, suchmetadata for each file may include the file name, a date of creation orlast modification of the file, any encryption information relating tothe file, and other information. In addition, metadata may be created bythe storage system for each file that links the file to a virtualcartridge. Using such metadata, the software provides to the hostcomputer an emulation of tape cartridges; however the file data is infact not stored in tape format, but rather in the system files, asdiscussed below. Storing the data in system files, rather than insequential cartridge format, may be advantageous in that it allows fast,efficient and random access to individual files without the need to scanthrough sequential data to find a particular file.

As discussed above, according to one embodiment, file data (i.e., userand/or system data) is stored on the back-up storage media as systemfiles, each system file including a header and data, the data being theactual user and/or system files. The header 202 of each system file 200includes a tape directory 206 that contains metadata linking the userand/or system files to virtual cartridges. The term “metadata” as usedherein refers not to user or system file data, but to data thatdescribes attributes of actual user and/or system data. According to oneexample, the tape directory may define, down to the byte level, thelayout of data on the virtual cartridges.

In one embodiment, the tape directory 206 has a table structure, asillustrated in FIG. 6. The table includes a column 220 for the type ofinformation stored (e.g., data, a file marker (FM), etc.), a column 222for the size of the disk blocks used in bytes, and a column 224 thatcounts the number of disk blocks in which the file data is stored. Thus,the tape directory allows the controller to have random (as opposed tosequential) access to any data file stored on back-up storage media 126.For example, referring to FIG. 6, the data file 226 may be quicklylocated on the virtual tape because the tape directory indicates thatthe data of file 226 begins one block from the beginning of the systemfile 200. This one block has no size because it corresponds to a filemarker (FM). File markers are not stored in the system file, i.e., filemarkers correspond to zero data. The tape directory includes filemarkers because they are used by conventional tapes and theback-up/restore application thus writes file markers along with datafiles and expects to see file markers when viewing a virtual cartridge.Therefore, file markers are kept track of in the tape directory.However, file markers do not represent any data and are therefore notstored in the data section of the system file. Thus, the data of file226 begins at the beginning of the data section of the system file,indicated by arrow 205 (see FIG. 5), and is 1024 bytes in length (i.e.,one disk block that is 1024 bytes in size). It should be appreciatedthat other file data may be stored in a block size other than 1024bytes, depending on the amount of data, i.e., the size of the data file.For example, larger data files may be stored using larger disk blocksizes for efficiency.

In one example, the tape directory may be contained in a “filedescriptor” that is associated with each data file backed-up onto thestorage system. The file descriptor contains metadata relating the datafiles 204 stored on the storage system. In one embodiment, the filedescriptor may be implemented in accordance with a standardized format,such as the tape archive (tar) format used by most UNIX based systems.Each file descriptor may include information such as the name of thecorresponding user file, the date the user file was created/modified,the size of the user file, any access restrictions on the user file,etc. Additional information stored in the file descriptor may furtherinclude information describing the directory structure from which thedata was copied. Thus, the file descriptor may contain searchablemetadata about a corresponding data file, as is discussed in more detailbelow.

From the point of view of the back-up/restore application, any virtualcartridge may contain a plurality of data files and corresponding filedescriptors. From the point of view of the storage system software, thedata files are stored in system files that may be linked to, forexample, a particular back-up job. For example, a back-up executed byone host computer at a particular time may generate one system file thatmay correspond to one or more virtual cartridges. Virtual cartridges maythus be of any size and may grow dynamically as more user files arestored on the virtual cartridges.

Referring again to FIG. 2, as discussed above, the storage system 170may include a synthetic full back-up software application 240. In oneembodiment, the host computer 120 backs-up data onto the emulated media134, forming one or more virtual cartridges. In some computingenvironments, a “full back-up,” i.e., a back-up copy of all data storedon the primary storage system in the network (see FIG. 1), may beaccomplished periodically (e.g., weekly). This process is typically verylengthy due the large amount of data that is to be copied. Therefore, inmany computing environments, additional back-ups, termed incrementalback-ups, may be performed between consecutive full back-ups, e.g.,daily. An incremental back-up is a process whereby only data that haschanged since the last back-up was executed (whether incremental orfull) is backed-up. Typically, this changed data is backed-up on a filebasis, even though frequently much of the data in the file has notchanged. Thus, incremental back-ups are typically much smaller, andtherefore much faster to accomplish, than are full back-ups. It is to beappreciated that although many environments typically execute fullback-ups once a week and incremental back-ups daily during the week,there is no requirement that such time frames are used. For example,certain environments may require incremental back-ups several times aday. The principles of the invention apply to any environment using fullback-ups (and optionally incremental back-ups), regardless of how oftenthey are executed.

During a full back-up procedure, the host computer may create one ormore virtual cartridges containing the back-up data that comprises aplurality of data files. For clarity, the following discussion willassume that the full back-up generates only one virtual cartridge.However, it is to be appreciated that a full back-up may generate morethan one virtual cartridge, and that the principles of the inventionapply to any number of virtual cartridges.

According to one embodiment, there is provided a method for creating asynthetic full back-up data set from one existing full back-up data setand one or more incremental back-up data sets. This method may obviatethe need to perform periodic (e.g., weekly) full back-ups, therebysaving the user considerable time and network resources. Furthermore, asknown to those of skill in the art, restoring data based on a fullback-up and one or more incremental back-ups can be a time consumingprocess because, for example, if the most recent version of a fileexists in an incremental back-up, the back-up/restore application willtypically restore the file based on the last full back-up and then applyany changes from the incremental back-ups. Providing a synthetic fullback-up, therefore, may have an additional advantage of allowing theback-up restore application to more quickly restore data files based onthe synthetic full back-up alone, without the need to perform multiplerestores from a full back-up and one or more incremental back-ups. It isto be appreciated that the phrase “most recent version” as used hereinrefers generally to the most recent copy of a data file (i.e., the mostrecent time that the data file was saved), whether or not the file has anew version number. The term “version” is used generally herein to referto copies of the same file which may be modified in some way or may havebeen saved multiple times.

Referring to FIG. 7, there is illustrated a schematic representation ofa synthetic full back-up procedure. The host computer 120 may execute afull back-up 230 at a first moment in time, for example, on a weekend.The host computer 120 may then execute subsequent incremental back-ups232 a, 232 b, 232 c, 232 d, 232 e, for example, on each day during theweek. The storage system 170 may then create a synthetic full back-updata set 234, as discussed below.

According to one embodiment, the storage system 170 may include asoftware application referred to herein as a synthetic full back-upapplication 240 (see FIG. 3). The synthetic full back-up application 240may be run on the storage system controller 122 (see FIG. 2) or may berun on the host computer 120. The synthetic full back-up applicationincludes software commands and interfaces necessary for creating thesynthetic full back-up data set 234. In one example, the synthetic fullback-up application may perform a logical merge of metadatarepresentations of each of the full back-up data set 230 and theincremental back-up data sets 232 to generate a new virtual cartridgethat contains the synthetic full back-up data set 234.

For example, referring to FIG. 8, the existing full back-up data set mayinclude user files F1, F2, F3 and F4. A first incremental back-up dataset 232 a may include user files F2′, a modified version of F2, and F3′,a modified version of F3. A second incremental back-up data set 232 bmay include user files F1′, a modified version of F1, and F2″, a furthermodified version of F2, and a new user file F5. Therefore, the syntheticfull back-up data set 234 formed from a logical merge of the fullback-up data set 230 and the two incremental data sets 232 a and 232 b,contains the latest version of each of user files F1, F2, F3, F4 and F5.As seen in FIG. 8, the synthetic full back-up data set thereforecontains user files F1′, F2″, F3′, F4 and F5.

Referring again to FIGS. 3 and 4, the file system software 146 maycreate a logical metadata cache 242 that stores metadata relating toeach user file stored on the emulated media 134. It is to be appreciatedthat the logical metadata cache is not required to be a physical datacache, but may instead be a searchable collection of data stored on thestorage media 126. In another example, the logical metadata cache 242can be implemented as a database. Where the metadata is stored in adatabase, conventional database commands (e.g., SQL commands) can beused to perform the logical merge of the full back-up data set and theone or more incremental back-up data sets to create the synthetic fullback-up data set.

In another embodiment, a portion of the metadata may be stored in adatabase, and another portion may be stored in storage system files. Forexample, back-up data set metadata, including back-up data set name anddata objects it comprises, may be included in the conventional database,while metadata specific to the data objects, such as, for example in thecase where the data object is a data file, data file size, securityinformation and location in primary storage may be included in storagesystem files. Storing metadata in this fashion enables flexibleretrieval of frequently queried data from a conventional database andpromotes system scalability by enabling faster storage of lessfrequently queried data in storage system files.

As discussed above, each data file stored on the emulated media 134 mayinclude a file descriptor that contains metadata relating to the datafile, including a location of the file on the back-up storage media 126.In one embodiment, the back-up/restore application running on the hostcomputer 120 stores data in a streaming tape format on the emulatedmedia 134. An example of a data structure 250 representing this tapeformat is illustrated in FIG. 9. As discussed above, the system filedata structure includes headers which may contain information about thedata file(s), such as the file descriptor for the data files, the datesof creation and/or modification of the files, security information, thedirectory structure of the host system from whence the file(s) came, aswell as other information linking the files to a virtual cartridge.These headers are associated with the data 254 which is actual user andsystem files that have been backed-up (copied) from the host computer,the primary storage system, etc. The system file data structure may alsooptionally include pads 256 which may appropriately align the nextheader to a block boundary.

As shown in FIG. 9, in one embodiment, the header data is located in thelogical metadata cache 242 to permit rapid searching and random accessto the otherwise sequential tape data format. The use of the logicalmetadata cache, implemented using the file system software 146 on thestorage system controller 122, allows translation of the linear,sequential tape data format, stored on the emulated media 134, into therandom-access data format stored on physical disks making up the back-upstorage media 126. The logical metadata cache 242 stores the headers 252which include the file descriptors for the data files, securityinformation which may be used to control access to the data files, as isdiscussed in more detail below, and pointers 257 to the actual locationsof the data files on the virtual cartridges and the back-up storagemedia 126. In one embodiment, the logical metadata cache stores datarelating to all the data files backed-up in the full back-up data set230 and each of the incremental data sets 232.

According to one embodiment, the synthetic full back-up applicationsoftware 240 uses the information stored in the logical metadata cacheto create a synthetic full back-up data set. This synthetic full back-updata set is then linked to a synthetic virtual cartridge, created by thesynthetic full back-up application 240. To the back-up/restoreapplication, the synthetic full back-up data set appears to be stored onthis synthetic virtual cartridge. As discussed above, the synthetic fullback-up data set may be created by performing a logical merge of theexisting full back-up data set and the incremental back-up data sets.This logical merge may include comparing each of the data files includedin each of the existing full back-up data set and the incrementalback-up data sets and creating a composite of the latest-modifiedversion of each user file, as discussed above in reference to FIG. 8.

According to one embodiment, the synthetic virtual cartridge 260includes pointers that point to locations of data files on other virtualcartridges, specifically, the virtual cartridges that contain theexisting full back-up data set and the incremental back-up data sets, asshown in FIG. 10. Considering the example given with respect to FIG. 8above, the synthetic virtual cartridge 260 includes pointers 266 thatpoint (indicated by arrows 268) to the locations in the existing fullback-up data set, on virtual cartridge 262, of user file F4 (because theexisting full back-up data set contained the latest version of F4) andto the location of, for example, user file F3′ in incremental data set232 a on virtual cartridge 264.

The synthetic virtual cartridge also includes a list 270 that containsthe identifying numbers (and optionally the names) of all the virtualcartridges that contain data to which the pointers 266 point. Thisdependent cartridge list 270 may be important for keeping track of wherethe actual data is and for preventing the dependent virtual cartridgesfrom being erased. In this embodiment, the synthetic full back-up dataset does not contain any actual user files, but rather a set of pointersthat indicate the locations of the user files on the back-up storagemedia 126. Therefore, it may be desirable to prevent the actual userfiles (stored on other virtual cartridges) from being deleted. This maybe accomplished in part by keeping a record (dependent cartridge list270) of the virtual cartridges that contain the data and protecting eachof those virtual cartridges from being over-written or deleted. Thesynthetic virtual cartridge may also include cartridge data 272 such as,the size of the synthetic virtual cartridge, its location on the back-upstorage media 126, etc. In addition, the synthetic virtual cartridge mayhave an identifying number and/or name 274.

According to another embodiment, the synthetic virtual cartridge mayinclude a combination of pointers and actual stored user files.Referring to FIG. 11, in one example, the synthetic virtual cartridgeincludes pointers 266 that point to locations of data files (the latestversions, as discussed above in reference to FIG. 9) in the existingfull back-up data set 230 on virtual cartridge 262. The syntheticvirtual cartridge may also include data 278 containing actual data filescopied from the incremental data sets 232, as indicated by arrows 280.In this manner, the incremental back-up data sets can be deleted afterthe synthetic full back-up data set 276 has been created, thereby savingstorage space. The synthetic virtual cartridges are relatively small asthey contain all or partly pointers rather than copies of all the userfiles.

It is to be appreciated that synthetic full back-ups may include anycombination of pointers and stored file data and are not limited to theexamples given above. For example, synthetic full back-ups may includepointers to data files for some files stored on certain incrementaland/or full back-ups and may include stored file data copied from otherexisting full and/or incremental back-ups. Alternatively still, asynthetic full back-up may be created based upon a prior full back-upand any relevant incremental back-ups that does not include anypointers, but rather includes the latest version of actual file datacopied from the appropriate full and/or incremental back-ups.

In one embodiment, the synthetic full back-up application software mayinclude a differencing algorithm that enables it to compare the user andsystem file metadata for each of the existing full back-up data set andthe incremental back-up data sets to determine where the latest versionof each of the data files is located. For example, a differencingalgorithm could be used to compare the dates of creation and/ormodification, the version number (if applicable), etc. between differentversions of the same data files in the different back-up sets to selectthe most recent version of the data file. However, users may often opena user file and save the file (thereby changing its data ofmodification) without actually changing any of the data inside the file.Therefore, the system may implement a more advanced differencingalgorithm that may analyze the data inside the system or user files todetermine whether the data has in fact changed. Variations of suchdifferencing algorithms and other types of compare algorithms may beknown to those skilled in the art. In addition, as discussed above,where the metadata is stored in a database format, database commandssuch as SQL commands can also be used to perform the logical merge. Theinvention may apply any of such algorithms to ensure that the mostrecent or latest version of each user file may be selected from allcompared existing back-up sets so as to properly create the syntheticfull back-up data set.

As should be appreciated by those skilled in the art, the synthetic fullback-up application enables full back-up data sets to be created andmade available without requiring the host computer to execute a physicalfull back-up. Not only does this avoid burdening the host computer withthe processor overhead of transferring the data to the back-up storagesystem, but in embodiments where the synthetic full back-up applicationis executed on the storage system, it significantly reduces theutilization of network bandwidth. As illustrated in FIG. 7, furthersynthetic full back-up data sets may be created using a first syntheticfull back-up data set 234 and subsequent incremental back-up data sets236. This may provide a significant time advantage in that files orobjects that are not frequently modified may not be frequently copied.Instead, the synthetic full back-up data sets may maintain pointers tothese files that have just been copied once.

Embodiments of the present invention also include computer systemsexecuting processes for removing redundant data from data objects. Suchremoval of redundant data is known in the art as “de-duplicating” data.FIG. 12 illustrates an example process 1200 for de-duplicating data froma data object according to one embodiment of the present invention. Thisprocess may be implemented using a single back-up storage system orwithin a distributed storage system environment, such as a gridenvironment as discussed above.

In general, a system conducting the process 1200 may cull throughmetadata associated with a series of data objects to identify those dataobjects that will be subject to further de-duplication process steps,such as, for example, data objects that are likely to share duplicatedata. The system may inspect the data objects identified for additionalprocessing to locate any redundant data. Further, the system mayconstruct copies of the identified data objects that point to a singlecopy of the redundant data and, optionally, validate the integrity ofthese copies. To reclaim storage capacity occupied by redundant data,the system may delete the originally identified data objects. Moredetails regarding the specific acts included in this process arediscussed below.

Still referring to FIG. 12, at step 1202, the data de-duplicationprocess 1200 begins. At step 1204, a system identifies data objects thatwill subject to further de-duplication processing. In one embodiment,the system may identify data objects that are likely to containredundant data. Various methods and metadata may be employed to makethis identification. For example, in one embodiment the physicallocation of a back-up data object in primary storage may indicate thatit is likely to have data with another back-up data object. Moreparticularly, if two back-up data objects originated from the sameprimary storage device, e.g. a particular server, then the data objectsmay be identified as likely including copies of redundant data.Similarly, in another embodiment, two data objects may be identified aslikely to have redundant data if both were created by a particularsoftware application. In still another embodiment, whether data objectswere stored as part of a full or incremental back-up policy may indicatea likelihood of redundant data. Identification of data objects that arelikely to contain duplicate data increases the overall efficiency of theprocess 1200 by enabling scarce computer resources, such as CPU cycles,to be focused on those data objects that will most benefit from removalof redundant data.

In another embodiment, a system may be configured to automaticallyinclude certain data objects in, or exclude certain data objects from,further de-duplication processing based on metadata associated withthese data objects. For instance, a system may be configured to includedata objects created by a particular software application inde-duplication processing. Likewise, a system may be configured toinclude data objects backed-up as part of a particular policy in furtherde-duplication processing. Conversely, the system may be configured toexclude all data objects backed-up by a particular policy and/orspecifically name data objects from further de-duplication processing.These configuration options enable system behavior to be tailored tosuit the particular needs of any client environment, thus promotingsystem performance and scalability.

At step 1206, the system conducting the process 1200 locates redundantdata in the data objects that were identified for further de-duplicationprocessing. This analysis may be accomplished by using metadata and/orby inspecting the actual contents of the identified data objects. In oneembodiment, data objects with similar metadata are assumed to comprisethe same data. For instance, if the data objects are data files and bothshare the same name, physical location in primary storage and CRC, hashor some other metadata generated during de-duplication processing, thenthe two data objects may be recorded as being redundant. Using metadatato identify redundant data provides several advantages. Using metadatapromotes efficiency because only the metadata of the data objects ratherthan the entirety of the data objects may be processed.

In another embodiment, data objects may be compared on a bit by bitbasis to guarantee redundancy before being so recorded. While this typeof comparison may be computing resource intensive, it also providesstrong assurance that any data identified as redundant is, in fact,completely redundant. This approach to determining redundancy may beuseful, for example, when handling data objects whose integrity isparticularly important, such as financial information.

In still another embodiment, some portion of the data included in thedata object is analyzed to establish redundancy of the entire object.For example, certain software applications may relegate modified data tocertain locations within data objects that they modify, e.g. at thebeginning or the end of the object. Thus, using this data distributionpattern, the system may focus its de-duplication processing on thoseportions of the data object that are more likely to be static, thusincrease system efficiency.

Embodiments of the present invention may employ a combination of thesetechniques to locate redundant data. More specifically, a system maydirect particular techniques to particular data objects based onmetadata such as that used to identify the data objects for furtherde-duplication processing above. This metadata may include, amongothers, location in primary storage, policy that caused the data objectto be backed-up and software application associated with the dataobjects. As with data object identification, the ability to tune thesystem with respect to manner of locating duplicate data promotes systemscalability and performance.

At step 1208, a system executing the process 1200 may createde-duplicated copies of previously identified data objects that includeredundant data. These de-duplicated copies may include little or noredundant data. In one embodiment, the identified data objects mayinclude, for example, virtual cartridges. In this instance, the systemmay create one or more de-duplicated virtual cartridges that, when fullyresolved, include all of the data included in the identified virtualcartridges. As with the synthetic virtual cartridges discussed above,these de-duplicated virtual cartridges may comprise both data objectsand pointers to data objects.

During the creation of these de-duplicated data copies, the system maystore copies of duplicated data within a particular data object andcreate and/or modify pointers within other data objects to store theduplicated data within those data objects. The system may follow variousmethodologies when storing the duplicated data and the pointers. In oneembodiment, the duplicated data is housed in the oldest data object, andpointers identifying the location of the duplicated data are stored inyounger data objects including the duplicated data. This technique,referred to in the art as backward referencing, is common where hashingindexes are built to summarize data objects for de-duplicationprocessing.

In another embodiment, the duplicated data is housed in the youngestdata object, and pointers identifying the location of the duplicateddata are stored in older data objects including the duplicated data.This technique may be termed forward referencing. Forward referencingincreases data restoration performance where data is restored from thelast back-up because reduced dereferencing of pointers is required toresolve all the data contained in the back-up data object. Thisincreased performance is particularly beneficial due to the fact thatthe most recent, i.e. youngest, back-up is usually used when data mustbe restored to primary storage.

FIGS. 13A, 13B and 13C illustrate both forward and backward referencingas described above. FIG. 13A shows the back-up data objects 1302 and1304 prior to de-duplication processing. For purposes of thisillustration, please assume the back-up data object 1302 was storedprior to the back-up data object 1304. The back-up data object 1302includes a unique data portion 1306 and a redundant data portion 1310A.The back-up data object 1304 includes a unique data portion 1308 and aredundant data portion 1310B.

FIG. 13B illustrates de-duplicated copies of the data objects 1302 and1304 under a forward referencing scheme. The data object 1304, which isthe more recently stored of the two, includes a copy of the redundantdata portion 1310B. The data object 1302, which is the less recentlystored of the two, includes a pointer 1312 which points to the redundantdata portion 1310B. Thus, after the de-duplicated copies are created,the younger data object includes a copy of the redundant data, and theolder data object includes a pointer to the redundant data in theyounger data object.

FIG. 13C illustrates de-duplicated copies of the data objects 1302 and1304 under a backward referencing scheme. The data object 1302, which isthe less recently stored of the two, includes a copy of the redundantdata 1310A. The data object 1302, which is the more recently stored ofthe two, includes a pointer 1312 which points to the redundant dataportion 1310A. Thus, after the de-duplicated copies are created, theolder data object includes a copy of the redundant data, and the youngerdata object includes a pointer to the redundant data in the older dataobject.

At step 1210, the system may compare the de-duplicated copies againstthe previously identified data objects to ensure data integrity has beenpreserved. This comparison may require dereferencing of data objectpointers and may include a bit by bit comparison of the data included inthe data objects. After this integrity check is performed, in oneembodiment, the system may swap the pointers that identify thede-duplicated copies and their respective previously identified dataobjects so that the de-duplicated data object becomes the primary dataobject and the previously identified data object may be deleted withoutdisrupting the integrity of any data objects that reference it. Thesystem may also make other adjustments to metadata to ensure itaccurately reflects the characteristics of the de-duplicated copy.

At step 1212, the storage capacity utilized by the previously identifieddata objects is reclaimed for use by other data objects. In oneembodiment, this may be accomplished by simply deleting the previouslyidentified data objects. At step 1214, process 1200 ends.

The process 1200 depicts a preferable sequence of events. Other actionscan be added, or the order of actions can be altered in the process 1200without departing from the spirit of the present invention. In oneembodiment, the process 1200 may be executed for each data objectincluded in a back-up storage system. In another embodiment, a systemmay execute the process 1200 for a subset of the data objects in theback-up storage system.

The process 1200 may be executed on demand or scheduled as a one-time orreoccurring process. Further subsets of the process 1200 may be executedwhen the space reclaimed by de-duplication will meet or exceed a certainthreshold. For example, in one embodiment the process 1200 may executeonly when de-duplication will free at least a specified number (e.g.,50) terabytes or a specified percentage (e.g., 25%) the utilized back-upstorage capacity. When implemented as event driven computing actions,the acts that comprise process 1200 may be executed in a distributedcomputing environment, such as a grid environment.

Thus, in summary, embodiments of the de-duplication process 1200 maydecrease the storage capacity required to maintain copies of back-updata and thus, decrease the amount of electronic media required to storeback-up data. Further, embodiments of the de-duplication process 1200may make efficient use of computing resources by using metadata tooptimize de-duplication processing. Finally, by storing de-duplicateddata in a forward referencing scheme, de-duplication can enhance theperformance of commonly used data restoration functionality.

As discussed above in reference to FIG. 3, the storage system may alsoinclude a software application referred to as the end-user restoreapplication 300. Thus, according to another embodiment, there isprovided a method for end users to locate and restore back-up datawithout IT staff intervention and without requiring any changes toexisting back-up/restore procedures and/or policies. In a typicalback-up storage system, the back-up/restore application running on thehost computer 120 is controlled by IT staff and it may be impossible orvery difficult for an end-user to access back-up data withoutintervention by the IT staff. According to aspects and embodiments ofthe invention, storage system software is provided that allows end usersto locate and restore their files via, for example, a web-based or otherinterface with the back-up storage media 126.

It is to be appreciated that, as with the synthetic full back-upapplication 240, the end-user restore application 300 may be run on thestorage system controller 122 (see FIG. 2) or may be run on the hostcomputer 120. The end-user restore application includes softwarecommands and interfaces necessary to allow an authorized user to searchthe logical metadata cache to locate, an optionally restore, back-upfiles from the back-up storage media 126.

According to one embodiment, there is provided software including a userinterface that is installed and/or executed on the user computer 136.The user interface may be any type of interface that allows a user tolocate files on the back-up storage media. For example, the userinterface may be a graphical user interface, may be web-based, or may bea text interface. The user computer is coupled to the storage system 170via a network connection 138 which may be, for example, an Ethernetconnection. Through this network connection 138, an operator of the usercomputer 136 can access the data stored on the storage system 170.

In one example, the end-user restore application 300 includes a userauthentication and/or authorization feature. For example, a user may beasked to login via the user interface on the user computer using ausername and password. The user computer may communicate the usernameand password to the storage system (e.g., to the end-user restoreapplication) which may use an appropriate user authentication mechanismto determine whether the user has access to the storage system. Someexamples of user authentication mechanisms that may be used include, butare not limited to, a MICROSOFT Active Directory server, a UNIX “yellowpages” server or a Lightweight Directory Access Protocol. The login/userauthentication mechanism may communicate with the end-user restoreapplication to exchange the user privileges. For example, some users maybe allowed to search only those files that have been created bythemselves or for which they have certain privileges or are identifiedas an owner. Other users such as, for example, system operators oradministrators may be allowed access to all back-up files, etc.

According to one embodiment, the end-user restore application uses thelogical metadata cache to obtain information about all the data filesbacked-up on the back-up storage media. The end-user restore applicationpresents to the user, via the user interface, a hierarchical directorystructure of the user's files sorted by, for example, back-up time/date,username, original user computer directory structure (that may have beenobtained when the files were backed-up), or other file characteristics.In one example, the directory structure presented to the user may varyaccording to the privileges enabled for that user. The end-user restoreapplication may accept browse requests (i.e., through the userinterface, the user may browse the directory structure to locate adesired file) or the user may search for a file by name, date, etc.

According to one embodiment, the user may restore back-up files from thestorage system. For example, once the user has located a desired file,as described above, the user may download the file from the storagesystem via the network connection 138. In one example, this downloadprocedure may be implemented in a manner comparable to any web-baseddownload, as known to those skilled in the art.

By allowing end users to access those files for which they havepermission to view/download, and by enabling such access through a userinterface (e.g., web-based technology), the end-user restore applicationcan enable user to search for and restore their own files without therebeing any need to alter any back-up policies or procedures.

It should be appreciated that although aspects of the present invention,such as the synthetic full back-up application and the end-user restoreapplication are described herein primarily in terms of software, itshould be appreciated that they may alternatively be implemented insoftware, hardware or firmware, or any combination thereof. Thus, forexample, embodiments of the present invention may comprise anycomputer-readable medium (e.g., a computer memory, a floppy disk, acompact disk, a tape, etc.) encoded with a computer program (i.e., aplurality of instructions), which, when executed, at least in part, on aprocessor of a storage system, performs the functions of the syntheticfull back-up application and/or the end-user restore application asdescribed in detail above.

In general summary, embodiments and aspects of the invention thusinclude a storage system and methods that emulate a conventional tapeback-up system but may provide enhanced functionality such as being ableto create synthetic back-ups and allowing end users to view and restoreback-up files. However, it should be appreciated that various aspects ofthe present invention may be used for other than the back-up of computerdata. Because the storage system of the present invention may be used toeconomically store vast amounts of data, and that stored data can beaccessed randomly, as opposed to sequentially, and at hard disk accesstimes, embodiments of the present invention may find use outside oftraditional back-up storage systems. For example, embodiments of thepresent invention may be used to store video or audio data representinga wide selection of movies and music and enable video and/or audio ondemand.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the scope of theinvention. Accordingly, the foregoing description and drawings are byway of example only.

What is claimed is:
 1. A method for removing redundant data from abackup storage system implementing a forward referencing scheme, themethod comprising: storing, by a back-up application, a more recentback-up data object at a first physical location, the more recentback-up data object having been backed-up more recently than a lessrecent back-up data object that is distinct from the more recent back-updata object and that is stored at a second physical location differentfrom the first physical location, the more recent back-up data objectincluding a first redundant portion and a first unique portion, the lessrecent back-up data object including a second redundant portion and asecond unique portion, the first unique portion including data differentfrom the second unique portion; identifying the less recent back-up dataobject created by the back-up application, the less recent back-up dataobject having been backed-up less recently than the more recent back-updata object; detecting that the first redundant portion is a copy of thesecond redundant portion; replacing the second redundant portion with apointer to the first redundant portion; and accessing, via the pointerto the first redundant portion by the back-up application, the morerecent back-up data object at the first physical location.
 2. The methodaccording to claim 1, wherein replacing the second redundant portionwith the pointer to the first redundant portion comprises: creating acopy of the less recent back-up data object excluding the secondredundant portion and including a pointer to the first redundantportion; and deleting the less recent back-up data object.
 3. The methodaccording to claim 2, further comprising validating that the copy of theless recent back-up data object represents the same data as the lessrecent back-up data object.
 4. The method according to claim 1, furthercomprising identifying at least one more recent characteristic of dataobject metadata; wherein storing the more recent back-up data objectincludes storing a more recent back-up data object associated with dataobject metadata having the at least one more recent characteristic; andwherein identifying the less recent back-up data object includesidentifying a less recent back-up data object associated with dataobject metadata having the at least one more recent characteristic. 5.The method according to claim 4, wherein identifying the at least onemore recent characteristic of data object metadata includes: identifyinga location in primary storage associated with the more recent back-updata object; and identifying a location in primary storage associatedwith the less recent back-up data object.
 6. The method according toclaim 4, wherein identifying the at least one more recent characteristicof data object metadata includes: identifying a software applicationassociated with the more recent back-up data object; and identifying asoftware application associated with the less recent back-up dataobject.
 7. The method according to claim 4, wherein identifying the atleast one more recent characteristic of data object metadata includes:identifying a back-up policy associated with the more recent back-updata object; and identifying a back-up policy associated with the lessrecent back-up data object.
 8. The method according to claim 4, whereinidentifying the at least one more recent characteristic of data objectmetadata includes: identifying at least one more recent characteristicof data object metadata that was stored while the more recent back-updata object was being backed-up; and identifying at least one morerecent characteristic of data object metadata that was stored while theless recent back-up data object was being backed-up.
 9. The methodaccording to claim 1, wherein detecting the first redundant portionincludes detecting a first redundant portion using metadata associatedwith the more recent back-up data object and metadata associated withthe less recent back-up data object.
 10. The method according to claim9, wherein detecting the first redundant portion using metadata includesdetecting a first redundant portion using metadata stored in arelational database.
 11. The method according to claim 1, whereinstoring the more recent back-up data object includes storing a morerecent data file; and wherein identifying the less recent back-up dataobject includes identifying a less recent data file.
 12. Acomputer-readable medium having computer-readable signals stored thereonthat define instructions that, as a result of being executed by acomputer, instruct the computer to perform the method of claim
 1. 13.The method according to claim 1, wherein the method is executed in agrid computing environment.
 14. The method according to claim 1, whereinthe method is executed on a backup storage system while data is notbeing backed-up to the back-up storage system.
 15. A method comprising:storing, by a back-up application, a more recent back-up data object ata first physical location, the more recent back-up data object beingassociated with a software application and having been backed-up morerecently than a less recent back-up data object that is distinct fromthe more recent back-up data object and that is stored at a secondphysical location different from the first physical location, the morerecent back-up data object including a first redundant portion and afirst unique portion, the less recent back-up data object including asecond redundant portion and a second unique portion, the first uniqueportion including data different from the second unique portion;identifying the less recent back-up data object created by the back-upapplication and associated with the software application, the lessrecent back-up data object having been backed-up less recently than themore recent back-up data object; detecting, using a pattern of datadistribution associated with the software application, that the firstredundant portion is a copy of the second redundant portion, the patternof data distribution being located within the more recent back-up dataobject and the less recent data back-up object; replacing the secondredundant portion with a pointer to the first redundant portion; andaccessing, via the pointer to the first redundant portion by the back-upapplication, the more recent back-up data object at the first physicallocation.
 16. A computer-readable medium having computer-readablesignals stored thereon that define instructions that, as a result ofbeing executed by a computer, instruct the computer to perform themethod of claim
 15. 17. A system comprising: back-up storage mediastoring a plurality of back-up data objects created by a back-upapplication and including a more recent back-up data object includingmore recent data and a less recent back-up data object that is distinctfrom the more recent back-up data object and that includes less recentdata, the more recent back-up data object including a first redundantportion and a first unique portion, the less recent back-up data objectincluding a second redundant portion and a second unique portion, thefirst unique portion including data different from the second uniqueportion; and a controller configured to: store the more recent back-updata object at a first physical location that is different from a secondphysical location at which the less recent back-up data object isstored; identify that the first redundant portion is a copy of thesecond redundant portion; replace the second redundant portion with apointer to the first redundant portion; and access via the pointer tothe first redundant portion the more recent back-up data object at thefirst physical location.
 18. The system according to claim 17, whereinthe controller is further configured to replace the second redundantportion by creating a copy of the less recent back-up data objectexcluding the second redundant portion and including a pointer to thefirst redundant portion.
 19. The method according to claim 4, furthercomprising identifying at least one less recent characteristic of dataobject metadata; wherein storing the more recent back-up data objectincludes storing a third portion of the more recent back-up data objectthat is associated with data object metadata having the at least oneless recent characteristic, the method further comprising excluding thethird portion from additional processing.
 20. The method according toclaim 1, wherein detecting the first redundant portion includesselecting a technique for locating redundant data based on metadataassociated with the more recent back-up data object.
 21. The methodaccording to claim 20, wherein selecting the technique for locatingredundant data includes selecting a technique for locating redundantdata that uses metadata associated with the more recent back-up dataobject.
 22. The method according to claim 20, wherein selecting thetechnique for locating redundant data includes selecting a technique forlocating redundant data that uses data included in the more recentback-up data object.
 23. The system according to claim 17, wherein themore recent data is newer than the less recent data.